The subject invention is directed to an apparatus and method for testing the burst strength of sheet material, such as paper.
Sheet material, such as paper, is manufactured in complex automated processes to achieve specified characteristics in accordance with the intended end use of the product. For example, sheet material may be produced to have a specified thickness, weight, surface texture and strength. The sheet may be a single integral ply or may be laminated from different materials. It is necessary to check the paper or other such sheet material being produced by the automated machinery to ensure that it complies with specifications. Generally a plurality of tests are conducted on the sheet material from each production run of such material. The plurality of tests are then averaged, compared and/or otherwise analyzed to assess compliance with specifications.
Burst strength is a parameter that is typically used to assess the strength of paper and other such sheet material. The typical prior art apparatus for testing burst strength comprises upper and lower platens each of which has a central aperture therein. The platens of the prior art apparatus are selectively movable toward and away from one another to enable placement of the test material therebetween. More particularly, the typical prior art burst testing apparatus includes a manual screw clamp which enables clamping pressure to be exerted by the upper platen of the prior art apparatus to clamp a product sample under test between the two platens. The prior art burst test apparatus further includes an expandable diaphragm mounted below the central aperture in the lower platen. A hydraulic pump is in communication with the expandable diaphragm, and is operative to direct hydraulic fluid at a specified and controlled rate toward the diaphragm. The hydraulic pressure causes the diaphragm to expand through the apertures in the platens and eventually to burst the sheet material clamped therebetween. The prior art burst testing apparatus further includes a gauge which measures the hydraulic pressure required to burst the sheet material being tested. The above described prior art apparatus is described, for example, in the publication entitled "PERKIN'S TESTERS" which was published by B. F. Perkins Company in 1983.
As noted above, the prior art burst testers are employed by subjecting the sheet material sequentially to a plurality of different tests. To perform this plurality of tests, an operator manually advances the sheet material through the prior art apparatus to selected locations at which the tests are sequentially performed. For example, a typical sample of material to be tested might be a narrow 5-15 foot long sheet, with some 20-40 tests being performed at linearly spaced apart locations along the length of the sheet of test material. The operator of the prior art apparatus will manually position and clamp the sheet, initiate each test and manually move the sheet material linearly intermediate successive tests. In other situations tests will be performed at a plurality of locations about the perimeter of a rectangular sheet. In these situations the operator again will manually initiate tests and translate the sheet of material intermediate successive tests.
The prior art apparatus for burst testing sheet material is considered to have several significant deficiencies. For example, the typical prior art apparatus requires the clamping pressure of the platens to be manually applied. This manual application of clamping pressure inherently creates the possibly of errors and differences between tests. A loosely clamped sheet of material can yield significantly higher burst strength requirements than a tightly clamped sheet of material.
Many prior art burst testers use a dial gauge for recording the burst pressure. Dial gauges are inherently inaccurate during either low burst pressure testing or high burst pressure testing. Under low burst pressure testing, the relatively rapid increase in pressure can cause the gauge to lag significantly behind the actual pressure being applied. With high burst pressure testing, a definite pop and associated vibration occur when the sheet material bursts, such that the pressure sensor is subjected to vibration and shock that can cause an incorrect reading on the dial gauge.
Prior art burst testers also do not automatically terminate the flow of hydraulic fluid after the burst has occurred. Rather, the operator of the prior art apparatus may be required to manually terminate the testing procedure. Ideally, the operator should react quickly to the audible pop generated at the instant the sheet material bursts. However, there is often a lag between the burst and the termination of the flow of hydraulic fluid. This increased flow of hydraulic fluid after the completion of the test will significantly shorten the life of the diaphragm, and in some instances will yield inaccurate pressure gauge readings.
As noted above, the prior art burst testers require the operator to manually advance the sheet material through the prior art burst tester between successive tests. If the sheet material is advanced too far, the operator will waste the test material. If the sheet material is advanced insufficiently, the operator will perform overlapping tests with the later test being meaningless or misleading.
In addition to the above described deficiencies, the prior art apparatus is very time consuming and requires the full attention of the operator. Thus, the prior art burst testing apparatus necessarily results in high labor costs and prevents the test operator from performing other necessary tasks at the testing facility.
In view of the above, it is an object of the subject invention to provide an automated burst testing apparatus that automatically provides a selected clamping pressure against the material being tested and that relieves the clamping pressure at the end of the test.
It is another object of the subject invention to provide a burst tester that can feed the sheet material being tested from one test to the next sequential test location on the sheet material.
It is an additional object of the subject invention to provide a burst tester with actuation means for automatically initiating a test when the sheet material is in a selected position.
A further object of the subject invention is to provide a burst tester that is operative to feed test material of different thicknesses.
Still another object of the subject invention is to provide a burst tester that is operative to terminate the flow of hydraulic fluid substantially at the instant of the burst.